The present invention relates to a novel and useful locking device for a door operator.
In the past, door locks have been employed in which only a key is able to lock or unlock the door. Typically, the key slot appears on one side of the door, normally exterior to the room being locked. A knob or lever appears on the opposite side of the door within the space secured, requiring a person within the space to exit the same and use a key to effect the locking or unlocking process. It is apparent that this system is very inefficient and very impractical since the person locking the space must exit the space to accomplish the unlocking or locking maneuver. Alternatively, the user may keep the door in the locked position but must open the door from the inside of the space by turning of lever, to let persons in and out of the space when necessary. The lever returns to its locked position after each unlocking due to a dead latch spring.
Many systems concerning door locks have been proposed in the past. For example, U.S. Pat. No. 4,236,396 shows a retrofitable lock which adds a deadbolt to the locking system in replacement of a conventional lock set.
U.S. Pat. No. 692,068 shows a combined lock and latch in which a thumb operated bar or spindle prevents draw back of a latch bolt.
U.S. Pat. No. 5,140,843 describes a lock conversion mechanism in which a key holder cup fits on the outside of a cylinder deadbolt to prevent the removal of the key once it is in the deadbolt.
U.S. Pat. Nos. 3,593,548, 4,673,202, 4,947,663, 5,003,803, 5,313,812, and 6,742,369 illustrate deadbolt keepers or holders that are mounted near the deadbolt latch and physically prevent rotation of the same when moved into an operative position.
U.S. Pat. Nos. 5,000,498 and 5,052,202 teach deadbolt latch holders that use a wedging mechanism directly to the latch or indirectly to the latch.
U.S. Pat. Nos. 4,798,069, 6,929,292 and 7,048,315 propose axillary locking mechanisms that employ a stop mounted at the door near a lever operator in order to interfere with the rotatable motion of the lever.
A locking device for a door which is easy to install on a conventional lock set and easily controls the lock state of the door would be a notable advance in the security field.